1. Field of the Invention
This invention pertains to the preparation of noncellular polyurethane sealant compositions containing an inorganic filler.
2. Description of the Prior Art
Those skilled in the art know that polyurethane sealant compositions can be prepared by mixing a polyol with an inorganic filler and reacting the mixture with a polyisocyanate. U.S. Pat. Nos. 3,450,653 and 3,484,517 are two examples of patents which disclose this teaching. The sealants disclosed in the prior art, however, have limited utility because their physical properties, such as tensile strength, hardness, brittleness, heat distortion, impact strength, and shrinkage resistance, have values which, although desirable for some uses, make them undesirable for other uses.
Applicants have discovered a method for preparing sealants which are strong, flexible, and shrinkage resistant. The sealants are prepared by mixing a polyether polyol or polyether polyol blend, having a branching density of 400 grams to 700 grams per branching unit, with inorganic fillers in an amount from 0.15 part to 0.7 part by weight per part of polyether polyol or polyether polyol blend. The mixture is reacted with a polyisocyanate to form the polyurethane sealant. Applicant is not aware of any reference which discloses this combination of ingredients or the significance of the combination. The polyols disclosed in U.S. Pat. Nos. 3,450,653 and 3,484,517 do not have branching densities of 400 grams to 700 grams per branching unit, and the amount of filler used in these processes exceeds the amount taught by the applicants.